The goal of this project is to understand the underlying physiological mechanisms of different involuntary movement disorders. We have continued characterization of inhibitory spinal reflex circuits in patients with stiffman syndrome (SMS), with a focus on serial performance of a selected battery of reflex studies at three points in a treatment trial. We have studied the somatosensory evoked potentials (SEP) elicited by muscle stretch reflexes in children with type III Gaucher disease (GD3) and healthy age-matched controls. Our results suggest that the SEP in GD3 children are abnormal even when they have no evidence of progressive myoclonus epilepsy. We are evaluating the nature of the positive and negative movements in patients with Sydenham's chorea. We have studied the post-excitatory inhibition (silent periods - SP) in children with Sydenham chorea with transcranial magnetic stimulation. We concluded that children with Sydenham chorea have a shortened SP which appears to normalize as the child recuperates. We are doing physiological tremor analysis, including spectral analysis of EMG and accelerometry, in persons in families with essential tremor and in persons with various neuropathies. These investigations should help with diagnosis of tremor as well as elucidate the pathophysiology. We studied physiologic tremor in normal controls and determined that 27% of the study population had evidence of the 8-12 HZ component of physiologic tremor. We are trying to develop physiological methods for assessment of psychogenic tremor. One test that looks promising is measuring the frequency spectrum of the tremor in one extremity while asking the patient to make movements with specified frequencies with the another extremity. In psychogenic tremor, the "tremor" may follow the voluntary movement frequency. Flexor reflex studies were done in normal volunteers to compare with patients with Restless legs syndrome (RLS) and Periodic limb movement disorder (PLMD), to test the hypothesis that PLMD of RLS results from enhanced excitability of the spinal cord. Normal subjects showed a dramatic sleep-related inhibition of the flexor reflex response. In contrast, in patients with RLS/PLMD there was significant desinhibition of the flexor reflex response during sleep. Sleep-related inhibition of the monosynaptic H reflex in patients was preserved. The EMG pattern of PLMs closely resembled that of the flexor reflex response. Our study shows abnormal excitability of the spinal cord mechanisms involved in the flexor reflex response in patients with RLS/PLMD. Our data suggest that PLMs in RLS originate in the spinal cord and are facilitated by the loss of supraspinal inhibition.